Quiz items endpoint: returns all the quiz items (currently, double answer and eliminate answer items) and the quantity the user owns. Additionally, it returns the user's gems so they can be shown on the mcq page.
Decrease by type endpoint: Decreases a user's item by user email and the item's type as a string (rather than its id). In hindsight, this might not have been necessary as we already have an id-based decrease endpoint, but it works the same since types must be unique for store items.
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